1. Field of the Invention
The invention relates to an apparatus and a method for manufacturing cement clinker, also referred to as clinker. The apparatus comprises a kiln for transforming the raw meal into clinker and at least a first heat exchanger for heating a fluid, in order to subsequently expand it in at least one turbine.
2. Description of Relevant Art
Clinker is produced by baking the raw meal in a kiln. This requires a temperature of about 1450° C. fuels such as coal, natural gas, petroleum, petroleum products (including plastic residues), paper or wood or other substitute fuels are burned in the kiln to produce this temperature.
Patent CH 689 830 A5 describes the production of clinker with simultaneous power generation. The preheated raw meal is baked in a rotary kiln to produce clinker as usual. The flue gases generated in the kiln are extracted from the kiln and the heat stored therein is used initially to preheat the raw meal. The flue gases cooled down in this process to about 600° C.-1200° C. are subsequently fed to a heat exchanger to produce superheated steam, which is then expanded in a turbine. The turbine drives a generator, such that the mechanical energy released during expansion is at least partially made available for use as electrical energy.
The published patent application DE 25 58 722 also describes a possibility for converting the heat energy contained in flue gases from the clinker process into electrical energy. This option uses the flue gases to preheat raw meal and produce steam. As usual, the raw meal is preheated in a heat exchanger tower with cyclone separators. A steam boiler for generating steam is arranged in the flue gas flow between the cyclone separators.
The raw meal usually consists of a mixture of limestone and clay or marl, often with iron ore and/or sand. In this way, chlorides, alkali metal compounds and sulphur compounds are also borne into the kiln with the raw meal. These impurities evaporate in the oven, leave it with the flue gas and then condense in the raw meal preheater and on the raw meal. A portion of the impurities are introduced back into the kiln with the raw meal, where they re-evaporate and leave the kiln with the flue gas to subsequently condense again. In this way, the impurities accumulate in the kiln and in the region of the raw meal preheater. This leads to a narrowing of the cross-section of the flue gas flow in the area where the contaminants condense. These impurities are therefore usually removed from the flue gas by means of a bypass system. These bypass systems remove a portion of the dust-laden kiln exhaust gases prior to entry into the raw meal preheater. However, there is a problem with subsequent processing of the dust accumulated from dedusting the bypass gases. The coarse dust can first be removed for instance from the bypass gas in a cyclone separator, before cooling the gas and then removing the fine dust in a fibrous filter. The coarse dust contains only a little chloride and can be fed into the kiln again. The fine dust has a high chloride content and can to a limited extent be added to the clinker, for instance during the cement milling process, without compromising the quality of the cement (cf. “A new chloride-bypass system with stable kiln operation and recycling of waste” Sutou et al., ZKG International, Vol. 54, No. 3, 2001, pp. 121-128). The problem of this solution is that the dust particles are needed as condensation nuclei and after coarse dust separation these condensation nuclei are no longer available in sufficient quantity.